Abstract

Measurements of the Faraday rotation in and have been made as a function of temperature in the range 100°–450°K at the helium‐neon laser wavelength of 1.15 μ. This wavelength lies on the edge of the window at the short‐wavelength absorption limit. Measurements were made on single‐crystal blocks of and up to 7 mm thick in applied fields of up to 10 kOe.

In the major contribution to the Faraday rotation at this wavelength is the dispersive part associated with absorption bands in the visible and near ir. This contribution reaches a maximum of 188°/cm at 280°K and can be fitted to the sublattice magnetization data of Anderson. For we find at 300°K and a very strong temperature dependence. In addition we observe a field‐dependent Faraday rotation of −3.8°/cm/kOe at 300°K. Extrapolation of the observed rotations to zero internal field removes he discontinuity in which otherwise appears at the compensation temperature (245°K). The zero‐field Faraday rotation may be analyzed in terms of three contributions: a nondispersive part arising from the exchange resonance, a dispersive part arising from the Fe3+ sublattices, and a dispersive contribution from the Tb3+ sublattice. Additional information on the Tb3+ contribution was obtained from Verdet constant measurements on and .